Optical device, image display apparatus and head-mounted display unit

ABSTRACT

Disclosed herein is an image display apparatus, including: a light source; and a scanning section adapted to scan a light beam emitted from the light source; the scanning section including (a) a first mirror, (b) a first light deflection section, (c) a second mirror, and (d) a second light deflection section; the second light deflection section including an external light receiving face; the second light deflection section having a plurality of translucent films provided in the inside thereof; the translucent films having a light reflectivity R 2  at a wavelength of the light beam which satisfies: R 2 ≦k ×{(P 2 /t 2 )×tan(ζ 2 )} 1/2  where k is a constant higher 0 but lower than 1, P 2  an array pitch of the translucent films, t 2  a thickness of the second light deflection section, and ζ 2  an angle formed between the light emitting face and the translucent films.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical device, an image display apparatusand a head-mounted display unit.

2. Description of the Related Art

A virtual image display apparatus or image display apparatus is knownand disclosed, for example, in JP-T-2005-521099 or Japanese PatentLaid-Open No. 2006-162767. In the virtual image display apparatus, atwo-dimensional image formed by an image forming apparatus is expandedby a virtual image optical system such that it is observed as anenlarged virtual image by an observer.

A virtual image display apparatus of the type described is schematicallyshown in FIG. 10. Referring to FIG. 10, the image display apparatus 200shown includes an image forming apparatus 201 including a plurality ofpixels arrayed in a two-dimensional matrix, and a collimate opticalsystem 202 for converting light emitted from the pixels of the imageforming apparatus 201 into parallel light. The image display apparatus200 further includes light guide means 203 which receives parallel lightfrom the collimate optical system 202, guides the parallel light thereinand emits the parallel light therefrom. The light guide means 203includes a light guide plate 204 from which incident light is emittedafter it propagates by total reflection in the inside of the light guideplate 204. The light guide means 203 further includes first deflectionmeans 205 formed, for example, from a single layer of a light reflectingfilm for reflecting light incident to the light guide plate 204 so thatthe light is reflected totally in the inside of the light guide plate204. The light guide section 203 further includes second deflectionmeans 206 formed, for example, from a light reflecting multilayer filmhaving a multilayer lamination structure for emitting light propagatedby total reflection in the inside of the light guide plate 204 from thelight guide plate 204. If the image display apparatus 200 having such aconfiguration as just described is used to configure, for example, ahead-mounted display (HD) unit, then the unit can be formed in alight-weighted small-sized form.

SUMMARY OF THE INVENTION

Incidentally, in the image display apparatus 200 described above, theimage forming apparatus 201 has a structure including a plurality ofpixels arrayed in a two-dimensional matrix and is configured, forexample, from a liquid crystal display apparatus of the transmissiontype or the reflection type such as a LCOS (Liquid Crystal On Silicon)liquid crystal display apparatus. Accordingly, it is difficult toachieve miniaturization of the image forming apparatus 201. Further, inthe image display apparatus 200 described, since it includes the imageforming apparatus 201 and the collimate optical system 202, also it isdifficult to achieve miniaturization and reduction in weight of theentire image display apparatus.

Accordingly, it is desirable to provide an image display apparatus whichcan be reduced in overall size and weight and a head-mounted displayunit to which the image display apparatus is applied.

An image display apparatus according to a first embodiment or a secondembodiment of the disclosure includes:

a light source; and

scanning means for scanning a light beam emitted from the light source;

the scanning means including

(a) a first mirror mounted for pivotal motion around a pivotal motionaxis thereof provided by a first axis extending in a first direction forreceiving the light beam emitted from the light source and incidentthereto,

(b) first light deflection means having an axial line extending along asecond direction different from the first direction for receiving thelight beam emitted from the first mirror and incident thereto at a firstincidence angle and emitting parallel light at a predetermined firstemergence angle with respect to the second direction depending upon thefirst incidence angle of the light beam by the pivotal motion of thefirst mirror,

(c) a second mirror mounted for pivotal motion around a pivotal motionaxis thereof provided by a second axis extending in a third directionand for receiving the parallel light emitted from the first lightdeflection means and incident thereto, and

(d) second light deflection means having an axial line extending along afourth direction different from the third direction for receiving theparallel light emitted from the second mirror and incident thereto at asecond incidence angle and emitting parallel light at a predeterminedsecond emergence angle with respect to the fourth direction dependingupon the second incidence angle of the parallel light by the pivotalmotion of the second mirror;

the second light deflection means including an external light receivingface provided in an opposed relationship to a light emitting faceprovided in parallel to the fourth direction for receiving externallight incident thereto;

the second light deflection means having a plurality of translucentfilms provided in the inside thereof.

Meanwhile, a head-mounted display unit according to the first embodimentor the second embodiment includes:

(A) a frame of the eyeglasses type adapted to be mounted on the head ofan observer; and

(B) an image display apparatus attached to the frame. The image displayapparatus of the head-mounted display unit is configured from the imagedisplay apparatus according to the first embodiment or the secondembodiment described above.

In the image display apparatus or the head-mounted display unitaccording to the first embodiment, the translucent films has a lightreflectivity R₂ at a wavelength of the light beam which satisfies:R ₂ ≦k×{(P ₂ /t ₂)×tan(ζ₂)}^(1/2)  (1)where k is a constant higher than 0 but lower than 1, P₂ an array pitchof the translucent films, t₂ a thickness of the second light deflectionmeans, and ζ₂ an angle formed between the light emitting face and thetranslucent films. It is to be noted that the light reflectivity isevaluated with vertically incident light. This similarly applies also inthe following description.

Meanwhile, in the image display apparatus or the head-mounted displayunit according to the second embodiment, a light reflectivity of each ofthe translucent films in a wavelength band other than the wavelength ofthe light beam is lower than that at the wavelength of the light beam.

On the other hand, an optical device according to the first embodimentor the second embodiment of the disclosure has:

a light receiving face provided in parallel to one direction and adaptedto receive light from a light source incident thereto;

a light emitting face provided in parallel to an axial line extending ina direction different from the one direction; and

an external light receiving face provided in an opposing relationship tothe light emitting face and adapted to receive external light incidentthereto;

the optical device having a plurality of translucent films providedtherein;

the translucent films being arrayed in parallel to each other in aspaced relationship from each other along the axial line and disposed inan inclined relationship to the axial line;

light from the light source incident to the light receiving face beingreflected by the translucent films and emitted from the light emittingface while external light incident from the external light receivingface is emitted from the light emitting face.

In the optical device according to the first embodiment, the translucentfilms has a light reflectivity R at a wavelength of the light from thelight source which satisfies:R≦k×{(P/t)×tan(ζ)}^(1/2)  (2)where k is a constant higher than 0 but lower than 1, P an array pitchof the translucent films, t a thickness of the optical device, and ζ anangle formed between the light emitting face and the translucent films.

Meanwhile, in the optical device according to the second embodiment, alight reflectivity of each of the translucent films in a wavelength bandother than the wavelength of the light from the light source is lowerthan that in the wavelength of the light from the light source.

The image display apparatus or the head-mounted display unit accordingto the first embodiment or the second embodiment of the disclosureincludes the first mirror, first light deflection means, second mirrorand second light deflection means, and converts and emits a light beamemitted from the light source into and as parallel light. Accordingly,an image forming apparatus itself formed, from example, from a liquidcrystal display apparatus is not required. Besides, there is nonecessity to produce, for example, a two-dimensional image once as anintermediate image in the inside of the scanning means. In other words,an image forming optical system is not required. Therefore, reduction insize of the light source or the scanning means and hence reduction insize and weight of the entire image display apparatus can beanticipated. In the image display apparatus or the head-mounted displayunit according to the first embodiment or the second embodiment, theparallel light originating from the light beam emitted from the lightsource and emitted finally from the second light deflection means isintroduced into the eyeballs of an observer. Then, the parallel lightpasses through the pupil, which usually has a diameter of approximately2 to 6 mm, of each eyeball and forms an image on the retina, throughwhich it is recognized as one pixel. This is because the light emittedfrom the second light deflection means is parallel light.

Then, such operations are repeated by a plural number of times to allowthe observer to recognize a two-dimensional image.

Besides, in the image display apparatus or the head-mounted display unitaccording to the first embodiment, the light reflectivity R₂ of thetranslucent films with regard to the wavelength of the light beamsatisfiesR ₂ ≦k×{(P ₂ /t ₂)×tan(ζ₂)}^(1/2)  (1).Meanwhile, in the optical device according to the first embodiment, thelight reflectivity R of the translucent films with regard to thewavelength of the light from the light source satisfiesR≦k×{(P/t)×tan(ζ)}^(1/2)  (2).Accordingly, the light intensity of the reflection of external lightwhen the external light is incident from the external light receivingface, comes to and is reflected by a translucent film and then comes toand is reflected by another translucent film can be reduced. As aresult, occurrence of ghosting can be suppressed.

On the other hand, in the image display apparatus, the head-mounteddisplay unit or the optical device according to the second embodiment,the light reflectivity of each of the translucent films in thewavelength band other than the wavelength of the light beam or the lightfrom the light source is lower than that at the wavelength of the lightbeam or the light from the light source. Accordingly, the reflection ofexternal light when the external light is incident from the externallight receiving face, comes to and is reflected by a translucent filmand then comes to and is reflected by another translucent film can bereduced. As a result, occurrence of ghosting can be suppressed.

The above and other features and advantages of the present inventionwill become apparent from the following description and the appendedclaims, taken in conjunction with the accompanying drawings in whichlike parts or elements denoted by like reference symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic views showing an image display apparatusaccording to a working example 1, and FIG. 1C is a schematic viewillustrating an incidence angle and an emergence angle;

FIGS. 2A and 2B are schematic views illustrating a state of a light beamand parallel light when an observer observes an image and a pixel at aleft lower corner of the image forms an image at a right upper portionof the retina;

FIGS. 3A and 3B are schematic views illustrating a state of a light beamand parallel light when an observer observes an image and a pixel at aright lower corner of the image forms an image at a left upper portionof the retina;

FIGS. 4A and 4B are schematic views illustrating a state of a light beamand parallel light when an observer observes an image and a pixel at aleft upper corner of the image forms an image at a right lower portionof the retina;

FIGS. 5A and 5B are schematic views illustrating a state of a light beamand parallel light when an observer observes an image and a pixel at aright upper corner of the image forms an image at a left lower portionof the retina;

FIG. 6 is a schematic view of a head-mounted display unit of a workingexample 2 as viewed from the front;

FIG. 7 is a schematic view of the head-mounted display unit of theworking example 2 as viewed from above;

FIG. 8 is a graph illustrating a wavelength dependency of a lightreflectivity of a translucent film which configures second lightdeflection means in a working example 3;

FIG. 9 is a schematic view showing a modification to the image displayapparatus of the working example 1;

FIG. 10 is a schematic view showing an image display apparatus of arelated art;

FIG. 11 is a schematic view illustrating a state in which a ghost imageappears when a light beam incident to first light deflection means froma first mirror is totally reflected by a first light emitting face ofthe first light deflection means; and

FIG. 12 is a schematic view illustrating another state in which a ghostimage appears when a light beam incident to the first light deflectionmeans from the first mirror is totally reflected by the first lightemitting face of the first light deflection means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, the embodiments of present invention is described indetail in connection with preferred working examples thereof withreference to the accompanying drawings. However, the present inventionis not limited to the working examples and various numerical values andmaterials specified in the description of the working examples are forillustrative purposes only. It is to be noted that description is givenin the following order.

1. General Description of the Optical Device According to the First andSecond Embodiments of the Invention, the Image Display ApparatusAccording to the First and Second Embodiments of the Invention and theHead-Mounted Display Unit According to the First and Second Embodimentsof the Invention

2. Working Example 1 (optical device and image display apparatusaccording to the first embodiment of the invention)

3. Working Example 2 (head-mounted display unit according to the firstembodiment of the invention)

4. Working Example 3 (optical device, image display apparatus andhead-mounted display unit according to the second embodiment of theinvention), Others

In the optical device, image display apparatus or head-mounted displayunit according to the first embodiment, the constant k can be set so asto satisfy 0.01≦k≦0.3, preferably set so as to satisfy 0.02≦k≦0.2, andmost preferably, for example, set to k=0.1. The optical device, imagedisplay apparatus or head-mounted display unit according to the firstembodiment including this preferred form may be configured such that

each of the translucent films reflects one of an S polarized lightcomponent and a P polarized light component but passes the other of thepolarized light components therethrough, and

the image display apparatus further includes a polarization sectionprovided on the external light receiving face side and adapted to passthe other of the polarized light components therethrough.

The optical device, image display apparatus or head-mounted display unitaccording to the second embodiment may be formed such that thewavelength band other than the wavelength of the light beam or the lightfrom the light source is defined as a wavelength band equal to or longerthan 420 nm but equal to or shorter than 680 nm except wavelengthswithin a range from λ₀−20 to λ₀+20 where λ₀ is a peak wavelength of thelight beam or the light from the light source whose unit is nm, and

the light reflectivity average value R_(WB-ave) in the wavelength bandother than the wavelength of the light beam or the light from the lightsource is lower than the light reflectivity average value R_(LS-ave)within the range from λ₀−20 to λ₀+20. In this instance, preferably0.01≦R_(WB-ave)/R_(LS-ave)≦1/1.41 is satisfied, and more preferably,0.05≦R_(WB-ave)/R_(LS-ave)≦0.5 is satisfied. Further, in the opticaldevice, image display apparatus or head-mounted display unit accordingto the second embodiment including those preferred forms, preferably thelight reflectivity at the wavelength of the light beam or the light fromthe light source is 5% or less upon vertical incidence. Further, theoptical device, image display apparatus or head-mounted display unitaccording to the second embodiment including those preferred forms maybe formed such that

each of the translucent films reflects one of an S polarized lightcomponent and a P polarized light component but passes the other of thepolarized light components therethrough, and

the image display apparatus further includes a polarization sectionprovided on the external light receiving face side and adapted to passthe other of the polarized light components therethrough.

The optical device, image display apparatus and head-mounted displayunit according to the first embodiment including the preferred formsdescribed above are sometimes referred to collectively and simply as“first embodiment of the disclosure.” Meanwhile, the optical device,image display apparatus and head-mounted display unit according to thesecond embodiment including the preferred forms described above aresometimes referred to collectively and simply as “second embodiment ofthe disclosure.” Further, the optical devices according to the first andsecond embodiments including the preferred forms described above aresometimes referred to collectively and simply as “optical device of thedisclosure.” Further, the image display apparatus according to the firstand second embodiments including the preferred forms described above aresometimes referred to collectively and simply as “image display deviceof the disclosure.” Further, the head-mounted display units according tothe first and second embodiments including the preferred forms describedabove are sometimes referred to collectively and simply as “head-mounteddisplay unit of the disclosure.” Furthermore, the first and secondembodiments of the disclosure are sometimes referred to collectively andsimply as “present disclosure.”

In the head-mounted display unit of the present disclosure,

the frame includes a front portion disposed in front of an observer, twotemple portions attached for pivotal motion to the opposite ends of thefront portion through hinges, and modern portions individually attachedto end portions of the temple portions;

the light source is disposed at an upper portion of each temple portionor the front portion;

the first mirror, first light deflection section and second mirror aredisposed at an upper portion of the front portion; and

the second light deflection section is disposed in an opposingrelationship to each of the pupils of the observer (or in other words,disposed at a position corresponding to an attached position of a lensof the frame of ordinary eyeglasses). Or, the light source itself may beprovided at each temple portion such that a light beam is introduced tothe front portion through an optical fiber. The arrangement described issuitable for a case in which the observer has a sufficient visual acuitywith the naked eye or in which contact lenses or the like are used.However, in the case where the observer uses ordinary eyeglasses forvisual correction, also it is possible to dispose the second lightdeflection section on the outer side of each lens of the eyeglasses.

Or the head-mounted display unit may be configured otherwise such thatthe first mirror, first light deflection section, second mirror andsecond light deflection section are disposed at an upper portion of thefront portion.

It is to be noted that the light receiving face through which the lightbeam or the light from the light source emitted from the first mirror isincident to the first light deflection section is referred to as “firstlight receiving face” for the convenience of description. Further, thelight receiving face through which the parallel light emitted from thesecond mirror is incident to the second light deflection section isreferred to as “second light receiving face” for the convenience ofdescription. Further, the light emitting face through which the parallellight is emitted from the first light deflection section is referred toas “first light emitting face” for the convenience of description.Furthermore, the light emitting face through which the parallel light isemitted from the second light deflection section is referred to as“second light emitting face” for the convenience of description.

The scanning section which configures the image display apparatus of thedisclosure and the head-mounted display units of the disclosureincluding the preferred configurations described above (such scanningsections are sometimes referred to collectively as “scanning sections ofthe present disclosure”) may be formed such that, where the firstemergence angle θ₀₋₁ of the parallel light emitted from the first lightdeflection section toward a direction away from the first mirror is anemergence angle of a positive value, as the first incidence angleθ_(I-1) of the light beam to the first light deflection sectionincreases, the first emergence angle θ₀₋₁ changes its direction fromthat of a negative value to that of a positive value. In this instance,where the second emergence angle θ₀₋₂ of the parallel light emitted fromthe second light deflection section toward a direction away from thesecond mirror is an emergence angle of a positive value, as the secondincidence angle θ_(I-2) of the parallel light to the second lightdeflection section increases, the second emergence angle θ₀₋₂ changesits direction from that of a negative value to that of a positive value.It is to be noted that the first incidence angle θ_(I-1) is defined asan angle formed between the light beam incident to the first lightdeflection section and the second direction. Meanwhile, the firstemergence angle θ₀₋₁ is defined as an angle formed between the parallellight emitted from the first light deflection section and a normal tothe first light emitting face of the first light deflection section.Similarly, the second incidence angle θ_(I-2) is defined as an angleformed between the light beam incident to the second light deflectionsection and the fourth direction. Meanwhile, the second emergence angleθ₀₋₂ is defined as an angle formed between the parallel light emittedfrom the second light deflection section and a normal to the secondlight emitting face of the second light deflection section. Further, thevalue of the first incidence angle θ_(I-1) formed between the seconddirection and the light beam which propagates in the inside of the firstlight deflection section and then advances toward the first lightemitting face of the first light deflection section is defined as apositive value. Similarly, the value of the second incidence angleθ_(I-2) formed between the fourth direction and the light beam whichpropagates in the inside of the second light deflection section and thenadvances toward the second light emitting face of the second lightdeflection section is defined as a positive value.

The scanning sections of the present disclosure including the preferredform described above may be configured such that the light beam incidentto the first light deflection section is expanded in the seconddirection by the first light deflection section, and the parallel lightincident to the second light deflection section is expanded in thefourth direction by the second light deflection section. Consequently,the parallel light obtained finally is in a form expandedtwo-dimensionally in the second and fourth directions.

The image display apparatus or the head-mounted display units of thepresent disclosure including the preferred forms and configurationsdescribed hereinabove may be configured such that an image is formedfrom an array of totaling P×Q pixels arrayed such that P pixels arearrayed along the second direction and Q pixels are arrayed along thefourth direction and the first incidence angle θ_(I-1) is defined inresponse to the position of the P pixels along the second directionwhile the second incidence angle θ_(I-2) is defined in response to the Qpixels along the fourth direction. By emission of a light beam once fromthe light source, one pixel of a display image is obtained finally.Accordingly, in order to display the P×Q pixels, emission of a lightbeam is carried out by P×Q times. The first and second mirrors have afunction of converting position information of a pixel into a kind ofangle information. The second direction and the fourth directionpreferably have a perpendicular relationship to each other.

Further, the image display apparatus or the head-mounted display unitsof the present disclosure including the preferred forms andconfigurations described hereinabove is configured preferably such thatthe number of times of pivotal motion, or in other words, theoscillation frequency, of the first mirror per unit time is higher thanthe number of times of pivotal motion or oscillation frequency of thesecond mirror per unit time. Or, the number of times of pivotal motionof the second mirror may be higher than those of the first mirror. Forpivotal motion of the first mirror or the second mirror, for example, asine wave signal, a rectangular wave signal or a sawtooth wave signalmay be input to a pivoting mechanism provided for the first mirror orthe second mirror. The frequency of the signal for driving the firstmirror is determined from the number of pixels along the seconddirection, the duty of the second mirror, the frame rate and so forthand is, for example, 15 Hz, 30 Hz, 60 Hz, 120 Hz, 180 Hz, 240 Hz or thelike. In the case where the first mirror or the second mirror isconfigured from a MEMS (Micro Electro Mechanical Systems) havingmicromirrors mounted for pivotal motion around one axis, for example,the pivotal motion of the first mirror at a high speed may be carriedout based on resonance while the pivotal motion of the second mirror ata low speed is carried out based on non-resonance. Or, the pivotalmotion of both of the first and second mirrors may be carried out basedon resonance.

Further, the image display apparatus or the head-mounted display unitsof the present disclosure including the preferred forms andconfigurations described hereinabove may be configured such that thefirst direction and the fourth direction coincide with each other orextend in parallel to each other and the second direction and the thirddirection coincide with each other or extend in parallel to each other,and the first and fourth directions and the second and third directionsare orthogonal to each other. In this instance, the image displayapparatus or the head-mounted display units may be formed such that animage observation position is positioned in the fifth direction withrespect to the second light deflection section, and the fifth directionhas an orthogonal relationship to the first and fourth directions andalso to the second and third directions. However, the directions may notnecessarily have a parallel or orthogonal relationship to each other.

In the disclosure including the preferred forms and configurationsdescribed above, a plurality of translucent films or half mirrors areprovided in the inside of the first light deflection section, andanother plurality of translucent films or half mirrors are provided inthe second light deflection section. The translucent films may beconfigured from metal films made of a metal including an alloy orconfigured from dielectric films of MgF_(X) or else from a multilayerlaminate structure in which a large number of conductor layer films arelaminated. The dielectric laminate films are configured for example,from a Si₃N₄ film as a high dielectric material and a MgF₂ film as a lowdielectric material or configured from a TiO₂ film, a NbO_(X) film or aTaO_(X) films as a high dielectric material and a SiO₂ film as a lowdielectric material. Formation of the translucent films or half mirrorscan be carried out by various physical vapor deposition methods (PVDmethods) including vacuum deposition and sputtering and various chemicalvacuum deposition methods (CVD methods) depending upon the material tobe used.

Further, in the disclosure including the preferred forms andconfigurations described above, a large number of translucent films mayhave an equal light reflectivity or may have different lightreflectivities depending upon the disposition position thereof in theinside of the first or second light deflection section. In the lattercase, preferably the translucent films in the first light deflectionsection are configured such that a comparatively high light reflectivityis provided to a translucent film positioned at a comparatively farposition from the first mirror. Meanwhile, preferably the translucentfilms in the second light deflection section are configured such that acomparatively high light reflectivity is provided to a translucent filmpositioned at a comparatively far position from the second mirror. Inother words, preferably he translucent films in the first lightdeflection section are configured such that a comparatively low lighttransmission factor is provided to a translucent film positioned at acomparatively far position from the first mirror. Meanwhile, preferablythe translucent films in the second light deflection section areconfigured such that a comparatively low light transmission factor isprovided to a translucent film positioned at a comparatively farposition from the second mirror. The light incidence angle dependency ofthe light transmission factor of the translucent films, that is, therelationship that, as the incidence angle of light incident to thetranslucent films increases, the light reflectivity increases, may beutilized. By gradually increasing the light reflectivity in this manner,it is possible to make the intensity of light reflected by a portion ofthe first light deflection section positioned spaced away from the firstmirror nearer to the intensity of light reflected by a portion of thefirst light deflection section positioned rear to the first mirror. Thissimilarly applies also to the second light deflection section.

In the disclosure, a light beam incident from the first mirror passesthrough the plural translucent films disposed in the inside of the firstlight deflection section and is reflected by the translucent films andthen emitted as parallel light from the first light deflection section.The parallel light incident from the second mirror passes through theplural translucent films disposed in the inside of the second lightdeflection section and is reflected by the translucent films and thenemitted as parallel light from the second light deflection section. Theangle of the translucent films in the first light deflection sectionwith respect to the second direction is equal among all translucentfilms and ranges from 30 degrees to 70 degrees, preferably from 40degrees to 60 degrees, and more preferably from 45 degrees to 55degrees. Similarly, the angle of the translucent films in the secondlight deflection section with respect to the fourth direction is equalamong all translucent films and ranges from 30 degrees to 70 degrees,preferably from 40 degrees to 60 degrees, and more preferably from 45degrees to 55 degrees. The array pitch of the translucent films may befixed or may differ. The second light deflection section is formed asthat of the see-through type or half-transmission or translucent type sothat an external field can be observed through the second lightdeflection section. The first light deflection section may have a lengthof 5 mm or more as a length thereof along the second direction, a heightof 0.5 mm or more as a length along the fourth direction, and athickness of 1.0 mm or more as a length along the fifth direction.Meanwhile, the second light deflection section may have a length of 5 mmor more as a length thereof along the second direction, a height of 5 mmor more as a length along the fourth direction, and a thickness of 0.5mm or more, for example, 2.5 mm to 5.0 mm, preferably 3.0 mm to 4.0 mmas a length along the fifth direction. Further, the second lightdeflection section may have an arrangement pitch of the translucentfilms of 0.5 mm to 1.5 mm.

Further, in the disclosure including the preferred forms andconfigurations described above, preferably an anti-reflection film isdisposed on the first light receiving face and the first light emittingface of the first light deflection section. Preferably, ananti-reflection film is disposed on the second light receiving face,second light emitting face and light emitting face. Here, theanti-reflection film (Anti Reflection Coating; ARC) may be formed fromat least one of materials selected from a group including, for example,silicon oxide (SiO_(x)), tantalum oxide (TaO_(X)), zirconium oxide(ZrO_(X)), aluminum oxide (AlO_(X)), chromium oxide (CrO_(X)), vanadiumoxide (VO_(X)), titanium oxide (TiO), zinc oxide (ZnO), tin oxide (SnO),hafnium oxide (HfO_(x)), niobium oxide (NbO_(X)), scandium oxide(ScO_(X)), yttrium oxide (YO_(X)), silicon nitride (SiN_(Y)), titaniumnitride (TiN), tantalum nitride (TaN), aluminum nitride (AlN), siliconoxynitride (SiO_(X)N_(Y)), aluminum fluoride (AlF_(X)), cerium fluoride(CeF_(X)), calcium fluoride (CaF_(X)), sodium fluoride (NaF_(X)), sodiumaluminum fluoride (Na_(Y)Al_(Z)F_(X)), lanthanum fluoride (LaF_(X)),magnesium fluoride (MgF_(X)), yttrium fluoride (YF_(X)) and zinc sulfide(ZnS_(X)). Or, the anti-reflection film may be configured in such astructure that at least two dielectric thin film layers of SiO, SiO₂,TiO₂, ZrO₂, Ta₂O₅ or Y₂O₃ are laminated like a laminate structure of,for example, a high reflectivity film/low reflectivity film/highreflectivity film/low reflectivity film, . . . . The anti-reflectionfilm can be formed by various PVD methods including vacuum depositionand sputtering or various CVD methods depending upon the material to beused.

In the disclosure including the preferred forms and configurationsdescribed above, the light source is preferably configured from a lightemitting element, particularly from a semiconductor laser device (LD), asolid-state laser, a light emitting diode (LED), a super luminescencediode (SLD), an organic EL light emitting device or an inorganic ELlight emitting device. Further, the light source in a wide senseincludes an optical fiber emitting end where the various types of lightsources are introduced into an optical fiber. Here, the light sourcepreferably includes a light emitting element for emitting red light,another light emitting element for emitting green light and a furtherlight emitting element for emitting blue light, and a multiplexingsection or color synthesis section. The multiplexing section multiplexesa red light beam, a green light beam and a blue light beam emitted fromthe light emitting elements into a single light beam. The multiplexingsection may be formed, for example, from a dichroic prism, a dichroicmirror, a cross prism, a polarizing beam splitter or a half mirror. Alight beam shaping section such as, for example, a collimate lens forconverting the light beam emitted from the light source into a parallellight beam may be disposed between the light source and the firstmirror. It is to be noted that, since this collimate lens merely passesone or a plurality of beams therethrough, such a great lens for passinga light source corresponding to an actual image therethrough as in acollimate optical system in the past is not demanded for the collimatelens. Further, in order to arrange the sectional shape of the light beamand in order to prevent appearance of undesirable scattered light orstray light, an aperture may be provided. The aperture may be disposedbetween the light source and the first mirror or between the firstmirror and the first light deflection section. The aperture may have acircular shape, a square shape, a rectangular shape, a regular hexagonalshape or a regular octagonal shape. The aperture may have an area from8×10⁻⁵ cm² (which corresponds, in the case of a circular shape, to adiameter of 0.1 mm) to 0.8 cm² (which corresponds, in the case of acircular shape, to a diameter of 10 mm). The intensity of the light beamemitted from the light source depends upon the brightness of an image tobe displayed and may be determined further taking the position of apixel in the image to be displayed into consideration. In particular,for example, in the case where the first incidence angle θ_(I-1) and thesecond incidence angle θ_(I-2) are small, since the number of thosetranslucent films through which the light beam or parallel light is topass is great, the intensity of the light beam to be emitted from thelight source may be increased.

The first mirror or the second mirror may be configured using, forexample, a MEMS having micromirrors mounted for pivotal motion aroundone axis, a galvano mirror, or a polygon mirror. Further, it is notalways necessary to use a mirror, but an arbitrary scanning section orscanning method may be used such as an electro-optical scanner, anacousto-optic scanner, movement of the collimate lens or pivotal motionof the light source itself. In particular, a first scanning section maybe used in place of the first mirror while a second scanning section isused in place of the second mirror.

The first light deflection section and the second light deflectionsection are made of a material transparent with respect to incidentlight. The material for the first light deflection section or the secondlight deflection section may be glass including optical glass such asquartz glass or BK7 or a plastic material such as, for example, PMMA, apolycarbonate resin, an acrylic-based resin, an amorphouspolypropylene-based resin, a styrene-based resin including an AS resin.It is to be noted that ordinary optical glass such as BK7 is high inworking accuracy and reliability and therefore is preferably used.Further, if a material having a high refractive index is used, then thethickness of the first light deflection section or the second lightdeflection section can be reduced, and preferably, the refractive indexis higher than 1.6.

The number of pixels may be determined based on specifications demandedfor the image display apparatus and may be, as a particular value of thenumber of pixels, 320×240, 432×240, 640×480, 854×480, 1024×768, 1366×768or 1920×1080.

The image display apparatus of the disclosure can be used to configure,for example, a head-mounted display unit and can achieve reduction inweight and size of the apparatus. The head-mounted display unit mayinclude one image display apparatus of the disclosure (monocular type)or two image display apparatus of the disclosure (binocular type).

As described hereinabove, the frame includes a front portion disposed infront of an observer, two temple portions attached for pivotal motion tothe opposite ends of the front portion through hinges, and modernportions individually attached to end portions of the temple portions.The frame further includes nose pads. When the entire head-mounteddisplay unit is watched, the assembly of the frame and the nose pads hasa structure substantially same as that of ordinary eyeglasses. The framemay be configured from a material same as that used for configureordinary eyeglasses such as a metal or an alloy, a plastic material or acombination of them. Also the nose pads may be have a knownconfiguration or structure.

From a point of view of the design of the head-mounted display unit orof facility in mounting of the head-mounted display unit, thehead-mounted display unit is preferably formed such that wiring linessuch as signal lines or power supply lines from one or two image displayapparatus extend from the end portions of the modern portions to anexternal circuit or control circuit through the inside of the templeportions and the modern portions. More preferably, the head-mounteddisplay unit is formed such that the image display apparatus includesheadphone portions, and wiring lines for the headphone portions from theimage display apparatus extend from the end portions of the modernportions to the headphone portions through the temple portions and theinside of the modern portions. The headphone portions may be, forexample, inner ear type headphone portions or canal type headphoneportions. More particularly, the wiring lines for the headphone portionsare preferably formed such that they extend from the end portions of themodern portions to the headphone portions in such a manner as to goround the rear side of the auricles or ear capsules.

WORKING EXAMPLE 1

The working example 1 relates to an image display apparatus and anoptical device according to the first embodiment of the presentinvention. The image display apparatus of the working example 1 isschematically shown in FIGS. 1A and 1B. In particular, FIG. 1A shows theimage display apparatus on a virtual plane, that is, on an XZ plane,including a second direction and a fifth direction. Meanwhile, FIG. 1Bshows the image display apparatus on another virtual plane, that is, ona YZ plane taken along line B-B in FIG. 1A and including a fourthdirection and the fifth direction. Further, FIG. 1C illustrate anincidence angle and an emergence angle. It is to be noted, however, thata translucent film is omitted in FIG. 1C. Further, it is shown in FIGS.1A to 1C and FIGS. 2A to 5B that the image display apparatus is disposedsuch that light is emitted in the positive direction of the Z axis froma first light deflection section 30 and light is emitted in the positivedirection of the Y axis, that is, in a downward direction, by a secondmirror 40. However, the image display apparatus may otherwise bedisposed such that, for example, light is emitted in the negativedirection of the Z axis from the first light deflection section 30 andlight is emitted in the positive direction of the Y axis, that is, in adownward direction, through reflection by the second mirror 40. It is tobe noted that a variation of light path by refraction of light incidentto and emergent from the first light deflection section, a second lightdeflection section and so forth is omitted in the figures.

The image display apparatus 10 of the working example 1 or the workingexample 3 hereinafter described includes a light source 11 and ascanning section for scanning a light beam emitted from the light source11. The scanning section includes:

(a) a first mirror 20 mounted for pivotal motion around an axis providedby a first axis 21 extending in a first direction and configured toreceive a light beam emitted from the light source 11 and incidentthereto;

(b) a first light deflection section 30 having an axis extending along asecond direction different from the first direction and configured toreceive the light beam emitted from the first mirror 20 and incident ata first incidence angle θ_(I-1) and emit parallel light at apredetermined first emergence angle θ₀₋₁ with respect to the seconddirection depending upon the first incidence angle θ_(I-1) of the lightbeam by pivotal motion of the first mirror 20;

(c) a second mirror 40 mounted for pivotal motion around an axisprovided by a second axis 41 extending in the third direction andconfigured to receive the parallel light emitted from the first lightdeflection section 30 and incident thereto; and

(d) a second light deflection section 50 having an axis extending alonga fourth direction different from the third direction and configured toreceive the parallel light emitted from the second mirror 40 andincident at a second incidence angle θ_(I-2) thereto and emit theparallel light having a predetermined second emergence angle θ₀₋₂ withrespect the fourth direction depending upon the second incidence angleθ_(I-2) of the parallel light by pivotal motion of the second mirror 40.

The second light deflection section 50 has an external light receivingface 54 provided in an opposing relationship to a light emitting face,that is, a second light emitting face 53, provided in parallel to thefourth direction and adapted to receive external light incident thereto.Further, a plurality of translucent films 31 each in the form of a halfmirror are provided in the inside of the first light deflection section30. Meanwhile, a plurality of translucent films 51 each in the form of ahalf mirror are provided in the inside of the second light deflectionsection 50.

Further, the optical device of the working example 1 or the workingexample 3 hereinafter described has:

a light incidence face, that is, a second light receiving face 52,provided in parallel to one direction, that is, to the third direction,and configured to receive light from a light source incident thereto;

a light emitting face, that is, a second light emitting face 53,provided in parallel to an axial line extending in a direction, that is,in the fourth direction, different from the one direction, that is, fromthe third direction; and

an external light receiving face 54 provided in an opposing relationshipto the light emergence face, that is, to the second light emitting face53, and configured to receive external light incident thereto.

Further, the optical device is configured such that,

a plurality of translucent films 51 are provided in the inside thereof,that

the translucent films 51 are arrayed in parallel to each other along theaxial line thereof and in a spaced relationship from each other and aredisposed in an inclined relationship to the axial line, and that

light from the light source incident to the light incidence face, thatis, to the second light receiving face 52, is reflected by thetranslucent films 51 and emitted from the light emitting face, that is,from the second light emitting face 53 while external light incidentfrom the external light receiving face 54 is emitted from the lightemitting face, that is, from the second light emitting face 53.

As seen in FIG. 1C and FIGS. 2A to 5B, it is assumed here that the firstemergence angle θ₀₋₁ of parallel light emitted from the first lightdeflection section 30 toward a direction away from the first mirror 20is an emergence angle of a positive value. In this instance, as thefirst incidence angle θ_(I-1) of a light beam to the first lightdeflection section 30 increases, the first emergence angle θ₀₋₁ changesits direction from that of a negative value to that of a positive value.Also it is assumed here that the second emergence angle θ₀₋₂ of parallellight emitted from the second light deflection section 50 toward adirection away from the second mirror 40 is an emergence angle of apositive value. In this instance, as the second incidence angle θ_(I-2)of parallel light to the second light deflection section 50 increases,the second emergence angle θ₀₋₂ changes its direction from that of anegative value to that of a positive value.

It is to be noted that, FIGS. 2A, 3A, 4A and 5A show the image displayapparatus on the virtual plane, that is, on the XZ plane, which includesthe second direction and the fifth direction similarly to FIG. 1A.Similarly, FIGS. 2B, 3B, 4B and 5B show the image display apparatus onthe virtual plane, that is, on the YZ plane, which includes the fourthdirection and the fifth direction similarly to FIG. 1B.

An image is formed from an array of totaling P×Q pixels arrayed suchthat P pixels are arrayed along the second direction and Q pixels arearrayed along the fourth direction. In particular, for example, P=640,Q=480, and the opposite angle is 28 degrees. The first incidence angleθ_(I-1) is defined in response to the position of the P pixels along thesecond direction, and the second incidence angle θ_(I-2) is defined inresponse to the Q pixels along the fourth direction. By emission of alight beam once from the light source 11, one pixel of a display imageis obtained finally. Accordingly, in order to display P×Q pixels, it isnecessary to emit P×Q light beams. Parallel light emitted from thesecond light deflection section 50 is incident to an eyeball of anobserver, passes through a pupil, which normally has a diameter ofapproximately 2 to 6 mm, of the eyeball, forms an image on the retinaand is recognized as one pixel. The observer can recognize atwo-dimensional image for one frame configured from P×Q pixels dependingupon a set of such operations, that is, upon the emission of the P×Qlight beams from the light source 11.

In the state illustrated in FIGS. 2A and 2B, that is, in a “state A,”when the observer watches the image, a pixel at a left lower corner ofthe image forms an image at a right upper portion of the retina.Meanwhile, in the state illustrated in FIGS. 3A and 3B, that is, in a“state B,” when the observer watches the image, a pixel at a right lowercorner of the image forms an image at a left upper portion of theretina. In the state illustrated in FIGS. 4A and 4B, that is, in a“state C,” when the observer watches the image, a pixel at a left uppercorner of the image forms an image at a right lower portion of theretina. In the state illustrated in FIGS. 5A and 5B, that is, in a“state D,” when the observer watches the image, a pixel at a right uppercorner of the image forms an image at a left lower portion of theretina. The first incidence angle θ_(I-1), first emergence angle θ₀₋₁,second incidence angle θ_(I-2) and second emergence angle θ₀₋₂ in thestates described are indicated in Table 1 below:

TABLE 1 State A State B State C State D First incidence minimum maximumminimum maximum angle θ_(I-1) First emergence minimum maximum minimummaximum angle θ₀₋₁ Second incidence minimum minimum maximum maximumangle θ_(I-2) Second emergence minimum minimum maximum maximum angleθ₀₋₂

A light beam incident to the first light deflection section 30 isexpanded in the second direction by the first light deflection section30, and the parallel light incident to the second light deflectionsection 50 is expanded in the fourth direction by the second lightdeflection section 50. Consequently, the parallel light obtained finallyis in a form expanded two-dimensionally in the second and fourthdirections.

The first mirror 20 and the second mirror 40 are configured, forexample, from a MEMS having micromirrors mounted for pivotal motionaround one axis. It is to be noted that the micromirrors configured fromsuch an MEMS may have a configuration and structure known in the art,and therefore, detailed description of the same is omitted herein. Here,the number of times of pivotal motion, or in other words, theoscillation frequency, of the first mirror 20 per unit time is higherthan the number of times of pivotal motion or oscillation frequency ofthe second mirror 40 per unit time. In particular, the number of timesof pivotal motion of the first mirror 20 per unit time is 21 kHz, andthe number of times of pivotal motion of the second mirror 40 per unittime is 60 Hz equal to the frame rate. It is to be noted that, while thepivotal motion of the first mirror 20 at a high speed is carried outbased on resonance and the pivotal motion of the second mirror 40 at alow speed is carried out based on non-resonance. However, both pivotalmotions may otherwise be carried out by resonance driving. Further, thearea of the second mirror 40 is greater than that of the first mirror 20because the light beam is expanded in the second direction by the firstlight deflection section 30. In particular, the first mirror 20 is sizedsuch that it is 2.0 mm long in the first direction and 2.8 mm long in adirection perpendicular to the first direction such that it has arectangular shape. Meanwhile, the second mirror 40 is sized such that itis 30 mm long in the third direction and 2.8 mm long in a directionperpendicular to the third direction such that it has a rectangularshape.

In the working example 1, the first and fourth directions coincide witheach other or in other words are parallel to each other, and the secondand third directions coincide with each other or in other words areparallel to each other. Further, the first and fourth directions and thesecond and third directions have a relationship orthogonal to eachother. Particularly, the image observation point is positioned in thefifth direction with respect to the second light deflection section 50and the fifth direction is perpendicular to the first direction and thefourth direction and also perpendicular to the second direction and thethird direction. More particularly, while the second and thirddirections are made the X direction and the first and fourth directionsare made the Y direction, the fifth direction is made the Z direction.However, the directions may otherwise be different from them, or theymay not have such a parallel or orthogonal relationship as describedabove.

The first light deflection section 30 and the second light deflectionsection 50 are made of optical glass such as BK7 whose refractive indexis 1.5168 at a wavelength of 587.6 nm. Here, the length, height andthickness of the first light deflection section 30, that is, a lengthTL₁ along the second direction, a length H₁ along the fourth directionand a length t₁ along the fifth direction of the first light deflectionsection 30, and the length, height and thickness of the second lightdeflection section 50, that is, a length TL₂ along the second direction,a length H₂ along the fourth direction and a length t₂ along the fifthdirection are set as given in Table 2 below. As described hereinabove,the first light deflection section 30 includes a plurality oftranslucent films 31 each in the form of a half mirror provided therein,and also the second light deflection section 50 has a plurality oftranslucent films 51 each in the form of a half mirror provided therein.In the working example 1, the pitches P₁ and P₂ along the second andfourth directions of the translucent films 31 and 51 are set as givenbelow. The translucent films 31 and 51 are formed at an equal pitch. Theangle of the translucent films 31 of the first light deflection section30 with respect to the second direction, that is, the angle ζ₁ of thefirst light deflection section 30 with respect to the second direction,is equal among all of the translucent films 31. Similarly, also theangle of the second light deflection section 50 with respect to thefourth direction of the translucent films 51, that is, the angle ζ₂ withrespect to the fourth direction, is equal among all of the translucentfilms 51.

TABLE 2 TL₁ =   30 mm H₁ =  3.0 mm t₁ =  7.0 mm TL₂ =   30 mm H₂ =   30mm t₂ =  5.0 mm P₁ = 0.75 mm ζ₁ = 49.0 degrees P₂ = 0.75 mm ζ₂ = 47.5degrees

The first light deflection section 30 and the second light deflectionsection 50 can be produced in the following manner. In particular, atranslucent film 31 or 51 is formed on the surface of an optical glassplate having a predetermined thickness by EB (Electron Beam) vapordeposition, and such resulting materials are adhered to and laminated oneach other. Then, the laminate is cut and polished such that thetranslucent films 31 or 51 may have a desired angle ζ₁ or ζ₂ withrespect to the second or fourth direction.

In the working example 1, the light source 11 is configured from asemiconductor laser device (LD). In particular, the light source 11 isconfigured from a light emitting element 11R in the form of asemiconductor laser device for emitting red light, a light emittingelement 11G in the form of a semiconductor laser element for emittinggreen light and a light emitting element 11B in the form of asemiconductor element for emitting blue light. A light beam of red,another light beam of green and a further light beam of blue emittedfrom the light emitting elements 11R, 11G and 11B are multiplexed into asingle light beam by a multiplexing unit or light synthesis unit. Themultiplexing unit is configured particularly from dichroic prisms 13. Itis to be noted that reference numerals 12 and 14 denote each areflecting mirror. While a light beam shaping unit in the form of acollimate lens for converting a light beam emitted from the light source11 into a parallel light beam is disposed between the light source 11and the fixed mirror 14, the collimate lens is omitted in the drawings.Further, an aperture not shown for shaping the sectional shape of thelight beam is provided between the light source 11 and the fixed mirror14. The aperture has a circular shape of a diameter of 1.0 mm.Accordingly, the sectional area of the light beam when one light beam isincident to the first mirror 20 is 7.9×10⁻³ cm².

It is to be noted that an anti-reflection film may be disposed or formedon a first light receiving face 32 and a first light emitting face 33 ofthe first light deflection section 30. Further, an anti-reflection filmmay be disposed or formed on the second light receiving face 52 and thesecond light emitting face 53 of the second light deflection section 50and the external light receiving face 54 of the second light deflectionsection 50 which opposes to the second light emitting face 53. Here, theanti-reflection films (ARC) are configured, for example, from a laminatefilm of MgF₂ and Si₃N₄.

Incidentally, as seen in a schematic sectional view of FIG. 11, part oflight incident to the second light deflection section 50 from theexternal light receiving face 54 passes through one of the translucentfilms 51 and is emitted from the second light emitting face 53.Meanwhile, the remaining part of the external light is reflected by thetranslucent film 51. Such external light is hereinafter referred to as“reflected external light” for the convenience of description. Thereflected external light comes upon a different one of the translucentfilms 51. Part of such reflected external light is reflected by thedifferent translucent film 51 and emitted to the outside. Such reflectedexternal light emitted from the translucent films 51 will form a ghostimage.

In the working example 1, where the array pitch of the translucentfilms, that is, of the translucent films 51, which configure the secondlight deflection section 50, is represented by P₂ the thickness of thesecond light deflection section 50 by t₂ and the angle of thetranslucent films 51 with respect to the second light emitting face 53by ζ₂ and k is a constant higher than 0 but lower than 1, the lightreflectivity R₂ of the translucent films with regard to the wavelengthof the light beam satisfiesR ₂ ≦k×{(P ₂ /t ₂)×tan(ζ₂)}^(1/2)  (1)Or, in the working example 1, where the array pitch of the translucentfilms 51 is represented by P (hereinafter referred to as “pitch P₂”),the thickness of the optical device by t (hereinafter referred to as“thickness t₂”) and the angle of the translucent films 51 with respectto the light emitting face by ζ (hereinafter referred to as “angle ζ₂”)and k is a constant higher than 0 but lower than 1, the lightreflectivity R (hereinafter referred to as “light reflectivity R₂”) ofthe translucent films with regard to the wavelength of the light fromthe light source satisfiesR≦k×{(P/t)×tan(ζ)}^(1/2)  (2)It is to be noted that, while, in the expressions (1) and (2), theentire second term of the right side is reduced to the power of ½, thisis because the external light which may cause ghosting is reflectedtwice by the translucent films 51 as seen in FIG. 11.

In the working example 1, more particularly the value of the constant kis set to k=0.1. Further, since

P₂=0.75 mm

t₂=5.0 mm

ζ₂=47.5 degrees

as indicated in Table 2 above,R ₂≦0.1×{(0.75/5.0)×tan(47.5)}^(1/2)=0.040is satisfied.

In the working example 1, in order to obtain the translucent films 51for achieving the light reflectivity of R₂=4.0% at the wavelength 530nm, a translucent film of a thickness 150 nm made of MgF₂ is used. It isto be noted that, while also the translucent films 31 which configurethe first light deflection section 30 is configured similarly in orderto simplify fabrication, the translucent films 31 of the first lightdeflection section 30 are not limited to those which satisfy theexpression (1) given hereinabove.

By setting the light reflectivity R₂ of the translucent films 51, forexample, to 4.0% in this manner, the light intensity of a ghost from thesecond light deflection section 50 can finally be made approximatelyequal to 1% of the light intensity of the external light incident to thesecond light deflection section 50. Consequently, occurrence of ghostingarising from incidence of external light to the second light deflectionsection 50 can be suppressed. Consequently, the light intensity of theexternal light which is incident to the second light deflection section50 from the external light receiving face 54, comes to and is reflectedby a translucent film 51, comes to and is reflected by anothertranslucent film 51, and to be emitted from the second light emittingface 53 can be reduced. As a result, occurrence of ghosting can besuppressed.

Besides, the image display apparatus of the working example 1 includesthe first mirror 20, first light deflection section 30, second mirror 40and second light deflection section 50 and emits a light beam emittedfrom the light source 11 as parallel light. Accordingly, there is nonecessity to produce, for example, a two-dimensional image once as anintermediate image in the inside of the scanning section. Further, animage forming apparatus itself configured, for example, from a liquidcrystal display apparatus is unnecessary. Therefore, reduction in sizeof the light source or the scanning section and besides reduction insize and weight as the image display apparatus can be anticipated.

It is to be noted that each translucent film 51 may be configured suchthat it reflects one of an S polarized light component and a P polarizedlight component and passes the other one of the S and P polarized lightcomponents therethrough. In particular, for example, each translucentfilm 51 may be configured such that it reflects an S polarized lightcomponent and passes a P polarized light component therethrough. Moreparticularly, each translucent film 51 is formed as a translucent filmof 40 nm thick made of MgF₂. Further, in place of disposition orformation of an antireflection film on the external light receiving face54, the second light receiving face 52 may be configured such that, onthe external light receiving face 54 side, more particularly on theexternal light receiving face 54, a polarizing element for passing theother polarized light component, that is, a P polarized light component,therethrough, more particularly a film formed by drawing dyed polyvinylalcohol, is provided. The extinction ratio of such a polarizing elementas just described is, for example, 10. Consequently, the external lightwhich is incident to the second light deflection section 50 from theexternal light receiving face 54 has a P polarized light component.Thus, if this external light comes to a translucent film 51, then thetranslucent film 51 reflects the S polarized light component while itpasses the P polarized light component therethrough. Therefore, theexternal light is transmitted through the translucent film 51 withoutbeing reflected by the translucent film 51. Accordingly, occurrence ofghosting arising from incidence of external light to the second lightdeflection section 50 can be suppressed with a higher degree ofcertainty.

WORKING EXAMPLE 2

The working example 2 relates to a head-mounted display (HMD) unitaccording to the first embodiment of the present invention. Inparticular, the working example 2 relates to a head-mounted display(HMD) unit which incorporates the image display apparatus according tothe first embodiment of the present invention, particularly the imagedisplay apparatus 10 described hereinabove in the description of theworking example 1. A schematic view of the head-mounted display unit ofthe working example 2 as viewed from the front is shown in FIG. 6.Further, a schematic view of the head-mounted display unit of theworking example 2 as viewed from above is shown in FIG. 7.

The head-mounted display unit of the working example 2 includes

(A) a frame 110 of the eyeglasses type for being mounted on the head ofan observer 70, and

(B) an image display apparatus 10.

It is to be noted that the head-mounted display unit in the workingexample 2 is formed as an apparatus of the binocular type including twoimage display apparatus 10.

The frame 110 includes a front portion 110A disposed in front of theobserver 70, two temple portions 112 attached for pivotal motion to theopposite ends of the front portion 110A through hinges 111, and modernportions 113 also called end cells or ear pads individually attached toend portions of the temple portions 112. Further, a light source 11, afirst mirror 20, a first light deflection section 30 and a second mirror40 are disposed at an upper portion of the front portion 110A, and asecond light deflection section 50 is disposed in an opposingrelationship to each of the pupils 71 of the observer 70. In particular,the second light deflection section 50 is attached to each of attachingmembers 110C formed from a transparent glass plate and disposed atpositions corresponding to lens attaching positions of a frame ofordinary eyeglasses. It is to be noted that the light source 11, firstmirror 20, first light deflection section 30 and second mirror 40 areaccommodated in each of housings 60 and are not shown in FIGS. 6 and 7.Further, nose pads 114 are attached to the front portion 110A. It is tobe noted that, in FIG. 7, the nose pad 114 is not shown. The frame 110is made of a metal or plastic.

Further, wiring lines 115 such as signal lines, power supply lines andso forth extend from the image display apparatus 10. The wiring lines115 extend through the inside of the temple portions 112 and the modernportions 113 to the outside from the end portions of the modern portions113 and are connected to an external circuit not shown. Further, each ofthe image display apparatus 10 includes a headphone portion 116, andheadphone portion wiring lines 117 extending from the individual imagedisplay apparatus 10 extend from the end portions of the modern portions113 to the headphone portions 116 through the inside of the templeportions 112 and the inside of the modern portions 113. Moreparticularly, the headphone portion wiring lines 117 extend from the endportions of the modern portions 113 to the headphone portions 116 insuch a manner as to go round the rear side of the auricles or earcapsules. By using such a configuration as just described, thehead-mounted display unit can be formed clear-cut without giving such animpression that the headphone portions 116 and/or the headphone portionwiring lines 117 are disposed disorderly.

WORKING EXAMPLE 3

The working example 3 relates to an image display apparatus, an opticaldevice and a head-mounted display unit according to the secondembodiment of the present invention.

In the image display apparatus or the head-mounted display unit of theworking example 3, a plurality of translucent films 51 are provided inthe inside of a second light deflection section 50 similarly as in theworking example 1 or the working example 2. Further, in the workingexample 3, the light reflectivity of the translucent films 51 in awavelength band other than the wavelength of a light beam is lower thanthat at the frequency of the light beam. Further, in the optical deviceof the working example 3, the light reflectivity of the translucentfilms 51 in the wavelength band other than the wavelength of the lightfrom the light source is lower than that at the wavelength of the lightfrom the light source.

Incidentally, part of external light incident to the second lightdeflection section 50 from the external light receiving face 54 passesthrough a translucent film 51 and is emitted from the second lightemitting face 53. On the other hand, as seen in a schematic sectionalview shown in FIG. 12 in addition to a schematic sectional view shown inFIG. 11, the remaining part of the external light which is reflected bya translucent film 51 may be totally reflected by the second lightemitting face 53 and returned to the inside of the second lightdeflection section 50 until it comes to a different translucent film 51.Part of such totally reflected external light passes through thedifferent translucent film 51 and is emitted to the outside. Meanwhile,the remaining part of such totally reflected external light is reflectedby the different translucent film 51 and emitted from the second lightemitting face 53, thereby to give rise to ghosting.

In the working example 3, the wavelength band other than the wavelengthof the light beam or the light from the light source is defined as awavelength band equal to or longer than 420 nm but equal to or shorterthan 680 nm except wavelengths within a range from λ₀−20 to λ₀+20 whereλ₀ is a peak wavelength of the light beam or the light from the lightsource. The unit of the peak wavelength is nm. In particular, the lightsource 11 is configured from a light emitting element 11R, a lightemitting element 11G and a light emitting element 11B each in the formof a semiconductor laser element. The light emitting element 11R emitslight of red whose wavelength λ₀(R) is λ₀(R)=620 nm; the light emittingelement 11G emits light of green whose wavelength λ₀(G) is λ₀(G)=530 nm;and the light emitting element 11B emits light of blue whose wavelengthλ₀(B) is λ₀(B)=460 nm. Accordingly, the wavelength band other than thewavelengths of the light beam or the light from the light source is 420nm to 440 m, 480 nm to 510 nm, 550 nm to 600 nm and 640 nm to 680 nm.Then, the light reflectivity average value R_(WB-ave) in the wavelengthband other than the wavelength of the light beam or the light from thelight source is lower than the light reflectivity average valueR_(LS-ave) within the range from λ₀−20 to λ₀+20. More particularly, thelight reflectivity average value R_(WB-ave) described is lower than thelight reflectivity average value R_(LS-ave)(B) within the range from 440nm to 480 nm, the light reflectivity average value R_(LS-ave)(G) withinthe range from 510 nm to 550 nm, and the light reflectivity averagevalue R_(Ls-ave)(R) within the range from 600 nm to 640 nm.

In particular, in the working example 3, the translucent films 31 and 51are configured from a dielectric multilayer film. More particularly, thetranslucent films 31 and 51 are formed by alternately laminating a MgF₂film of a thickness of 120 nm having a refractive index of 1.38 and aSi₃N₄ film of another thickness of 190 nm having another refractiveindex of 2.00 into nine layers. A graph illustrating a wavelengthdependency of the light reflectivity of such a translucent film as justdescribed is illustrated in FIG. 8.

Here, the light reflectivity average value R_(WB-ave) of the lightreflectivity illustrated in FIG. 8 in the wavelength band describedabove isR _(WB-ave)=0.001(0.1%).On the other hand, an average value R_(LS-ave) of the light reflectivityaverage values R_(LS-ave)(R), R_(LS-ave) (G) and R_(LS-ave)(B) isR _(LS-ave)=0.005(0.5%).Therefore,R _(WB-ave) /R _(LS-ave)=0.2.

For example, the second light deflection section 50 in which translucentfilms having a light reflectivity average value of 0.01 (1%) in thewavelength band equal to or longer than 420 nm but equal to or shorterthan 680 nm are provided and the second light deflection section 50 inwhich the translucent films 51 in the working example 3 are provided arecompared with each other. In this instance, since external light whichmay cause ghosting is reflected twice by the translucent films 51 asdescribed hereinabove in the description of the working example 1, thelight intensity of the ghost is, for example, in the wavelength bandother than the wavelength of the light beam or light from the lightsource,(R _(WB-ave))²/(0.01)²=0.01.Thus, by providing the translucent films 51 in the working example 3 inthe second light deflection section 50, sufficient reduction of thelight intensity of a ghost can be achieved.

In this manner, in the working example 3, the light reflectivity of thetranslucent films in the second light deflection section in thewavelength band other than the wavelength of the light beam or the lightof the light source is lower than that of the wavelength of the lightbeam or the light from the light source. Accordingly, the reflection ofexternal light when the external light is incident from the externallight receiving face, comes to and is reflected by a translucent filmand then comes to and is reflected by another translucent film can bereduced. As a result, occurrence of ghosting can be suppressed.

It is to be noted that, except that the translucent films are differentin configuration and structure, the configuration and structure of theoptical device, image display apparatus and head-mounted display unit ofthe working example 3 can be made similar to the configuration and thestructure of the optical devices, image display apparatus andhead-mounted display units described hereinabove in connection with theworking example 1 and the modification to the working example 1 whichincludes a light polarizing unit as well as the working example 2.Therefore, detailed description of them is omitted herein to avoidredundancy. The reflection factor of the translucent films 31 whichconfigure the first light deflection section 30 may be similar to thatof the translucent films 51 which configure the second light deflectionsection 50 or may have a fixed value without depending upon thewavelength.

While the present invention is described above based on the preferredworking examples thereof, the present invention is not limited to theworking examples. The configuration and the structure of the imagedisplay apparatus, optical devices and head-mounted display unitsdescribed in connection with the working examples are illustrative andcan be altered suitably. While, in the working examples, thehead-mounted display unit is of the binocular type which includes twoimage display apparatus, alternatively it may be formed as that of themonocular type which includes a single image display apparatus. Further,the light source may be configured from a single kind of light emittingelement such as, for example, a light emitting element which emits lightof red, another light emitting element which emits light of green or afurther light emitting element which emits light of blue. Further, alight source may be provided in a temple portion of the head-mounteddisplay unit, or a first mirror, a first light deflection section, asecond mirror and a second light deflection section may be disposed atan upper portion of a front portion of the head-mounted display unit.While, in the working example, a large number of translucent films havean equal light transmission factor, the light transmission factor may bemade different depending upon the arrangement position in the inside ofthe first light deflection section or the second light deflectionsection. In particular, for example, in the first light deflectionsection, the light reflectivity of a translucent film positioned spacedaway from the first mirror is set comparatively high, but in the secondlight deflection section, the light reflectivity of a translucent filmpositioned spaced away from the second mirror is set comparatively high.In other words, in the first light deflection section, the lighttransmission factor of a translucent film positioned spaced away fromthe first mirror is set comparatively low, but in the second lightdeflection section, the transmission factor of a translucent filmpositioned spaced away from the second mirror is set comparatively low.More specifically, for example, the value of the light reflectivity of atranslucent film positioned at the farthest position from the first orsecond mirror is set to 1.1 to five times the value of the lightreflectivity of another translucent film which is positioned adjacentthe first or second mirror. While, in the working examples, light isemitted in the positive direction of the Z axis from the first lightdeflection section 30 and is emitted in the positive direction of the Yaxis, that is, in the downward direction, by the second mirror 40.However, the arrangement of the first light deflection section 30 andthe second mirror 40 is not limited this, but they may otherwise bearranged such that, for example, light is emitted in the negativedirection of the Z axis from the first light deflection section 30 andis emitted in the positive direction of the Y axis, that is, in thedownward direction, by the second mirror 40 as seen in FIG. 9.

It is to be noted that also it is possible to configure a light beamexpansion apparatus from the scanning section in the embodiments of thepresent invention. In particular, a light beam expansion apparatus forexpanding a light beam emitted from a light source two-dimensionally ina second direction and a fourth direction and emitting the light beam asparallel light includes

(a) a first mirror mounted for pivotal motion around a pivotal motionaxis thereof provided by a first axis extending in a first direction andadapted to receive the light beam emitted from the light source andincident thereto;

(b) a first light deflection section having an axial line extendingalong a second direction different from the first direction and adaptedto receive the light beam emitted from the first mirror and incidentthereto at a first incidence angle and emit parallel light at apredetermined first emergence angle with respect to the second directiondepending upon the first incidence angle of the light beam by thepivotal motion of the first mirror;

(c) a second mirror mounted for pivotal motion around a pivotal motionaxis thereof provided by a second axis extending in a third directionand adapted to receive the parallel light emitted from the first lightdeflection section and incident thereto; and

(d) a second light deflection section having an axial line extendingalong a fourth direction different from the third direction and adaptedto receive the parallel light emitted from the second mirror andincident thereto at a second incidence angle and emit parallel light ata predetermined second emergence angle with respect to the fourthdirection depending upon the second incidence angle of the parallellight by the pivotal motion of the second mirror.

Further, in the light beam expansion apparatus, the second lightdeflection section is provided in an opposing relationship to a lightemitting face provided in parallel to the fourth direction and adaptedto receive external light incident thereto, and a plurality oftranslucent films are provided in the inside of the second lightdeflection section similarly as in the first embodiment of the presentinvention. Or, the light reflectivity of the translucent films in thewavelength band other than the wavelength of the light beam is lowerthan that at the wavelength of the light beam similarly as in the secondembodiment of the present invention.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2010-144453 filed in theJapan Patent Office on Jun. 25, 2010, the entire content of which ishereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alternations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalent thereof.

What is claimed is:
 1. An image display apparatus comprising: a lightsource; and scanning means for scanning a light beam emitted from saidlight source; said scanning means including (a) a first mirror mountedfor pivotal motion around a pivotal motion axis thereof provided by afirst axis extending in a first direction for receiving the light beamemitted from said light source and incident thereto, (b) first lightdeflection means having an axial line extending along a second directiondifferent from the first direction for receiving the light beam emittedfrom said first mirror and incident thereto at a first incidence angleand emitting parallel light at a predetermined first emergence anglewith respect to the second direction depending upon the first incidenceangle of the light beam by the pivotal motion of said first mirror, (c)a second mirror mounted for pivotal motion around a pivotal motion axisthereof provided by a second axis extending in a third direction andadapted to receive the parallel light emitted from said first lightdeflection means and incident thereto, and (d) second light deflectionmeans having an axial line extending along a fourth direction differentfrom the third direction for receiving the parallel light emitted fromsaid second mirror and incident thereto at a second incidence angle andemitting parallel light at a predetermined second emergence angle withrespect to the fourth direction depending upon the second incidenceangle of the parallel light by the pivotal motion of said second mirror;said second light deflection means including an external light receivingface provided in an opposed relationship to a light emitting faceprovided in parallel to the fourth direction for receiving externallight incident thereto; said second light deflection means having aplurality of translucent films provided inside thereof; said translucentfilms having a light reflectivity R₂ at a wavelength of the light beamwhich satisfies:R ₂ ≦k×{(P ₂ /t ₂)×tan(ζ₂)}^(1/2) where k is a constant greater than 0but lower than 1, P₂ an array pitch of said translucent films, t₂ athickness of said second light deflection means, and ζ₂ an angle formedbetween said light emitting face and said translucent films.
 2. Theimage display apparatus according to claim 1, wherein k =0.1.
 3. Theimage display apparatus according to claim 1, wherein each of saidtranslucent films reflects one of an S polarized light component and a Ppolarized light component but passes the other of the polarized lightcomponents therethrough; said image display apparatus further comprisingpolarization means provided on said external light receiving face sidefor passing the other of the polarized light components therethrough. 4.The image display apparatus according to claim 1, wherein P×Q pixelsincluding P pixels along the second direction and Q pixels along thefourth direction are arrayed in an image; and the first incidence angleis defined in response to a position of the P pixels along the seconddirection and the second incidence angle is defined in response to aposition of the Q pixels along the fourth direction.
 5. The imagedisplay apparatus according to claim 1, wherein the first direction andthe fourth direction coincide with each other and the second directionand the third direction coincide with each other, and the first andfourth directions and the second and third directions are orthogonal toeach other.
 6. A head-mounted display unit, comprising: (A) a frame ofthe eyeglasses type adapted to be mounted on the head of an observer;and (B) an image display apparatus attached to said frame; said imagedisplay apparatus including light source and scanning means for scanninga light beam emitted from said light source; said scanning meansincluding (a) a first mirror mounted for pivotal motion around a pivotalmotion axis thereof provided by a first axis extending in a firstdirection and adapted to receive the light beam emitted from said lightsource and incident thereto, (b) first light deflection means having anaxial line extending along a second direction different from the firstdirection for receiving the light beam emitted from said first mirrorand incident thereto at a first incidence angle and emitting parallellight at a predetermined first emergence angle with respect to thesecond direction depending upon the first incidence angle of the lightbeam by the pivotal motion of said first mirror, (c) a second mirrormounted for pivotal motion around a pivotal motion axis thereof providedby a second axis extending in a third direction and adapted to receivethe parallel light emitted from said first light deflection means andincident thereto, and (d) second light deflection means having an axialline extending along a fourth direction different from the thirddirection for receiving the parallel light emitted from said secondmirror and incident thereto at a second incidence angle and emittingparallel light at a predetermined second emergence angle with respect tothe fourth direction depending upon the second incidence angle of theparallel light by the pivotal motion of said second mirror; said secondlight deflection means including an external light receiving faceprovided in an opposed relationship to a light emitting face provided inparallel to the fourth direction for receiving external light incidentthereto; said second light deflection means having a plurality oftranslucent films provided inside thereof; said translucent films havinga light reflectivity R₂ at a wavelength of the light beam whichsatisfies:R ₂ ≦k×{(P ₂ /t ₂)×tan(ζ₂)}^(1/2) where k is a constant greater than 0but lower than 1, P₂ an array pitch of said translucent films, t₂ athickness of said second light deflection means, and ζ₂an angle formedbetween said light emitting face and said translucent films.
 7. Anoptical device having: a light receiving face provided in parallel toone direction and adapted to receive light from a light source incidentthereto; a light emitting face provided in parallel to an axial lineextending in a direction different from the one direction; and anexternal light receiving face provided in an opposing relationship tosaid light emitting face and adapted to receive external light incidentthereto; said optical device having a plurality of translucent filmsprovided therein; said translucent films being arrayed in parallel toeach other in a spaced relationship from each other along the axial lineand disposed in an inclined relationship to the axial line; light fromsaid light source incident to the light receiving face being reflectedby said translucent films and emitted from said light emitting facewhile external light incident from said external light receiving face isemitted from said light emitting face; said translucent films having alight reflectivity R at a wavelength of the light from said light sourcewhich satisfies:R ≦k×{(P/t)×tan(ζ)}^(1/2) where k is a constant greater than 0 but lowerthan 1, P an array pitch of said translucent films, t a thickness ofsaid optical device, and ζan angle formed between said light emittingface and said translucent films.